1. Field of the Invention
The present invention relates to an ink jet recording apparatus for recording an image by ejecting ink onto a recording medium. More particularly, the present invention relates to an ink jet recording apparatus for use in information processing equipment such as printers, copying machines, computers, and word processors.
2. Description of the Related Art
As one of conventional recording apparatuses, an ink jet recording apparatus is known in which a recording medium is intermittently fed in a recording section, and each time the feed is interrupted, ink droplets are ejected from a recording head over a certain width in a direction perpendicular to the feed direction, thereby recording an image.
In an ink jet recording apparatus, unless the spacing between a nozzle surface of a recording head, which ejects ink in a recording section, and a recording medium is maintained to be very small with high accuracy, there occur a deflection of an image due to an arrival failure of ejected ink droplets, and a smear due to contact between the recording head and the recording medium.
In some of ink jet recording apparatuses, therefore, a carriage holding a recording head is scanned with high accuracy using a guide shaft of good straightness, and a recording medium is attracted onto a flat platen under a vacuum sucking action. Generally, in the apparatus using such a sucking platen, a vacuum pump, a fan or the like is employed as a negative pressure generating source, and air in an enclosed space below the platen is evacuated to the outside to create a negative pressure in the space.
Recently, to meet a demand for recording an image in the frameless form without surrounding margins as with a borderless photograph, there has been proposed an apparatus in which ink is ejected over a range greater than the width of a recording medium to form a frameless image.
FIG. 9 is a perspective view of a platen and thereabout of such a conventional recording apparatus. Referring to FIG. 9, a recording medium 201 is supplied to a recording section in the apparatus from the direction of arrow K. A feed roller 202 is able to grip the recording medium 201 in cooperation with pinch rollers 203, 204 and 205, and to intermittently feed the recording medium 201 with high accuracy through coupling to a driving system (not shown) that rotates the feed roller.
A platen 206 is arranged such that its guide surface 206a supports thereon the recording medium 201 fed to the platen 206 by the feed roller 202 in a surface-to-surface contact relation. A plurality of openings 210 are formed in the guide surface 206a and communicated with a space formed within the platen 206 via air passages. When the space formed in the platen 206 below the guide surface 206a is evacuated to create a negative pressure by a vacuum pump or a fan, the recording medium 201 is attracted onto the guide surface 206a of the platen 206 through the openings 210 under a vacuum sucking action. Thus, the recording medium 201 can maintain a certain level of planeness.
A guide shaft 231 is arranged such that its axis extends in a direction, perpendicular to the feed direction of the recording medium 201 and parallel to the guide surface 206a of the platen 206.
A carriage 232 is fitted over the guide shaft 231 and coupled to a linearly moving means (not shown) for movement in directions of arrows L and Lxe2x80x2, i.e., in the main scan direction. An ink jet recording head is provided in the carriage 232 and has an ink ejection surface positioned to face the guide surface 206a of the platen 206. During the movement of the recording head in the main scan direction, the spacing between the ink ejection surface and the recording medium 201 is maintained with high accuracy as long as the recording medium 201 is attracted onto the platen 206 to take a satisfactory flat posture.
The carriage 232 receives an electrical signal from a main control unit via a cable (not shown) and transmits the received signal to the recording head for ejecting ink. In accordance with the ejection signal received during the movement in the main scan direction, the recording head forms a long strip of image on the recording medium 201 lying over the platen 206 with a width corresponding to a row of ejection nozzles provided in the recording head. By repeating the above recording step the predetermined number of times whenever the recording medium 201 is intermittently fed by the feed roller 202, an image of one page can be formed on the recording medium 201.
The plurality of circular openings 210 formed in the guide surface 206a of the platen 206 are arrayed at an appropriate pitch so that the recording medium 201 is stably attracted onto the platen 206 through the plurality of openings 210 under vacuum suction. Further, ink recovery ports 211, 212 for frameless recording are formed in the platen 206 at positions respectively corresponding to both ends 201a, 201b of the recording medium 201 in the width direction thereof. Ink ejected outside the width of the recording medium 201 is recovered through the ink recovery ports 211, 212 to prevent the ink from directly depositing on the guide surface 206a of the platen 206.
FIG. 10 is a sectional view for explaining a situation in which the recording head ejects ink near the widthwise end 201a of the recording medium 201 in the frameless recording. Because the ends 201a of the recording medium 201 projects like a pent roof, there occurs an air eddy as indicated by one-dot-chain lines.
The conventional recording apparatus described above, therefore, has the following problems. The occurrence of an air eddy causes ink to scatter in the form of mists in addition to main ink droplets ejected from the recording head. The scattered mists may deposit on the backside of the recording medium and give rise to a backside smear.
Also, such ink mists move in a floating condition with the movement of the scanned carriage. When the recording medium 201 sometimes rises, even though slightly, away from the platen 206, the ink mists are attracted to the left, as viewed in FIG. 10, by sucking forces acting through the suction openings 210 and deposit on the platen surface adjacent to the ink recovery port 211. Then, the deposited ink mists adhere to the backside of the recording medium and also gives rise to a backside smear even slightly.
Further, when a leading end of the recording medium is positioned above the ink recovery port at the initial point of recording operation of one image, ink mists occur at the same time as ink ejection from the recording head and go around the leading end of the recording medium, thereby disturbing air streams. That tendency increases and intensifies turbulence as the recording medium is fed with the progress of recording and covers the ink recovery port at a greater rate. As a result, the ink mists may deposit on the backside of the leading end of the recording medium and give rise to a backside smear at the leading end of the recording medium.
Moreover, the recording head performs preliminary ejection for ejecting ink, which resides in nozzles and has an increased viscosity, before starting to eject the ink onto the recording medium. The ink is ejected in the preliminary ejection toward an ink receiver having the same structure as the ink recovery port. Upon the preliminary ejection, an air eddy occurs around an ejected ink stream due to air resistance and reaction caused within the ink receiver. This leads to a possibility that the ink may scatter to the surroundings of the ink receiver and give rise to a smear.
In addition, the ink mists and the ejected ink tend to deposit at corners of wall surfaces of both the ink recovery port and the ink receiver due to a capillary phenomenon, and gradually grow with the repeated recording operation to such an extent as impeding air streams in the ink recovery port and the ink receiver. Therefore, unwanted ink, such as ink mists, may scatter and deposit on the backside of the recording medium, thereby causing a backside smear.
In view of the state of the art set forth above, it is an object of the present invention to provide an ink jet recording apparatus which can perform high-quality recording without causing a backside smear of a recording medium even in frameless recording where an image is recorded in full size until reaching lengthwise and widthwise ends of the recording medium with respect the feed direction.
Another object of the present invention is to provide an ink jet recording apparatus which can prevent ink from scattering when preliminary ejection is performed.
Still another object of the present invention is to provide an ink jet recording apparatus which has a stream baffling structure provided corresponding to each of opposite ends of a recording medium to prevent the occurrence of turbulence caused in an ink sucking recovery port when the ends of the recording medium are subjected to an ink jet recording, and hence which can avoid ink mists from going around to the backside of the recording medium.
Still another object of the present invention is to provide an ink jet recording apparatus for ejecting ink from a recording unit to a recording medium to record an image, the apparatus comprising an ink recovery section for recovering ink ejected outside an end of the recording medium, a negative pressure generating unit for generating a pressure in the ink recovery section lower than the atmospheric pressure, and an air stream passage for communicating the ink recovery section and the negative pressure generating unit with each other.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.